Practical - DNA Extraction (OCR GCSE Biology A (Gateway))

Extraction of DNA from Fruit

Observing DNA in the Lab

• This is not a core practical but still a worthwhile experiment

• The molecular appearance of DNA is very familiar, but can we actually extract this important molecule from cells and look at it?

• DNA can actually be extracted from fruit using some basic classroom equipment

• Fruits that have relatively large amounts of DNA in their cells

  • Strawberries, bananas and kiwis can be used

Method

• Mash the fruit and mix this into a beaker containing a solution of detergent (e.g. washing up liquid) and salt

  • The detergent breaks down the cell membranes (and the nuclear membranes), causing the fruit cells to release their DNA

  • The salt causes the DNA to stick together

• Filter the mixture into a test tube

  • This removes any debris (big, insoluble bits of cell) from the mixture

• Gently add some ice-cold ethanol to the filtrate (the filtered mixture) by pouring the ethanol slowly down the side of the test tube

  • This causes the DNA to precipitate (i.e. to come out of solution) as DNA is not soluble in cold alcohol

• The DNA will appear as a stringy white precipitate (a solid)

• If needed, this precipitate can be carefully extracted using a glass rod

A simple method for extracting DNA from fruit